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Biology 102

Biology 102. Gene expression (cont.)/ Begin Cellular reproduction. Lecture outline. Gene expression and regulation (cont.) Mutations Regulation of gene expression Cellular reproduction Types of cellular reproduction Mitosis vs. meiosis Overview of mitosis/cell cycle Steps of mitosis.

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Biology 102

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  1. Biology 102 Gene expression (cont.)/ Begin Cellular reproduction Chapter 1

  2. Lecture outline • Gene expression and regulation (cont.) • Mutations • Regulation of gene expression • Cellular reproduction • Types of cellular reproduction • Mitosis vs. meiosis • Overview of mitosis/cell cycle • Steps of mitosis Chapter 1

  3. Mutations • Mutations and protein synthesis • Source of mutations • Exposure to mutagens • Errors in replication and transcription • Results of mutation: Changes in DNA can result in changes in the proteins for which they code Chapter 1

  4. Examples of Mutations Chapter 1

  5. Effects of mutations • Some are insignificant • More than one codon for most amino acids • Third nucleotide position is often not important • G-U-n = valine • U-C-n = serine • C-G-n = arginine • Some are Harmful • Frameshift, missense or nonsense Chapter 1

  6. Effects of mutations • Mutations can be beneficial! • Altered proteins may be more effective than originals • Mutations are the source of genetic variation • Significance to ability to evolve X-men! Chapter 1

  7. Gene expression • Individual cells express only a small fraction of their genes • Gene expression is influenced by developmental stage and environment • How is gene expression regulated? Chapter 1

  8. Regulation of gene expression (cont.) • Types of regulation • Frequency of transcription • Turned on or off at promotor region • Rate/amount of mRNA translated • Some mRNA stable, others break down • Activation/inactivation of proteins • Lifespan of the protein Chapter 1

  9. Types of cell reproduction • BinaryFission • (bacteria) DNA replicated Membrane added Chapter 1

  10. False-Color EM of Dividing Bacterium Nuclearmaterial Division plane Cell wall Cytoplasm Chapter 1

  11. Asexual reproduction by mitosis New individuals Chapter 1

  12. Asexual Reproduction by Mitosis Chapter 1

  13. Functions of Mitosis in animals Organs Fertilized egg (zygote) Multicell stage Mitotic cell division & differ-entiation Mitotic cell division Tissues Chapter 1

  14. Mitosis, Meiosis, and the Sexual Cycle Chapter 1

  15. G1: Growth cytokinesis telophase S: Synthesis of DNA; chromosomes duplicated anaphase celldivision Mitosis metaphase prophase interphase G2: Growth Focus on Mitosis G0: nondividing Chapter 1

  16. Interphase • DNA exists as chromatin: The chromosomes (blue) are in the thin, extended state • Wrapped around protein • DNA is 2 meters long! • Replicated while in this form • The microtubules (red) extend outward from the nucleus to all parts of the cell. Chapter 1

  17. Prophase • DNA condenses into distinct chromosomes • Additional winding • Relationship of genes and chromosomes • Diploid: Homologous pairs of chromosomes • Sister chromatids held together by centromere at this stage • Don’t confuse diploid with sister chromatids! • Mitotic spindle forms from microtubules • Chromosomes attached • Nuclear membrane disappears Chapter 1

  18. Metaphase • Chromosomes are lined up in midline • The chromosomes have moved along the spindle microtubules • Homologous chromosomes aligned “head to toe” • At end of metaphase, centromeres release sister chromatids Chapter 1

  19. Anaphase • Sister chromatids have separated, and one set of chromosomes moves along the spindle microtubule to each pole of the cell. • Cell still diploid, but chromosomes now are only single chromatids • Cell is always diploid throughout this process! Chapter 1

  20. Telophase • The chromosomes have gathered into two clusters, one at the site of each future nucleus. • Chromosomes begin to decondense back to chromatin • Nuclear membrane forms • Followed by cytokinesis • Cytoskeleton “pinches” cell into two parts • Plants form new cell wall Chapter 1

  21. Cytokinesis of a Ciliated Cell Daughter Cells Cleavage Furrow Chapter 1

  22. Cytokinesis in Plants Vesicles fuse to form cell wall and membranes Complete separation of daughter cells Chapter 1

  23. Mitosis: Review Nucleolus disappears; Nuclear envelope breaks down Duplicated chromosomes remain elongated Chromosomes condense and shorten LateInterphase EarlyProphase LateProphase Metaphase Centrioles have also been duplicated Centrioles begin to move apart; Spindle forms Microtubules attach to kinetochores Kinetochores align at cell’s equator Chapter 1

  24. Mitosis: Review (cont.) One set of chromosomes; Begin unwinding Free spindle fibers push poles apart Cytoplasm divided along equator NextInterphase Anaphase Telophase Cytokinesis Each daughter gets 1 nucleus & half of cytoplasm Spindle disappears; Nucleolus reappears Chromatids become independent chromosomes Nuclear envelope re-forms Chapter 1

  25. How do cells “know” when to stop dividing? • Cell senescence • Cells are programmed to stop dividing. • Cells of older people programmed to stop dividing earlier (50x for newborn cells, 30x for aged person's cells) • Growth control • Cell division inhibited by contact with other "like" cells. • Ex: wound closure. • Cancer cells do not exhibit growth control. Something has gone haywire. They keep growing. Chapter 1

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